1. Field of the Invention
This invention relates to a semiconductor file memory and a storage system which uses the semiconductor file memory, and more particularly to the improvement of a data transfer system intended for a file memory which necessitates a smaller number of connection pins, stores transferred data in variable data length and reads out data in variable data length.
2. Discussion of Related Art
Generally, an external storage of information processor, such as a magnetic recording medium or file memory, operates to exchange information with the host information processor in either parallel data transmission mode or serial data transmission mode, the latter being the case of serial data processing for a sequential file as disclosed in SCSI or the like. Information transaction based on serial transmission generally uses block transfer.
Conventional file memories, which use the parallel I/O interface, have increased the number of address signal lines as semiconductor memory devices have become more capacious, resulting in an increased number of connector pins of the file memories. In parallel data transmission, the number of connection lines increases in proportion to the number of bits of transmission, and at the same time the volume of data transmission in a unit time length also increases. In contrast, serial data transmission is advantageous in a smaller number of connection lines required, but it is limited in the volume of data transmission in a unit time length.
A file memory with an increased number of connection pins suffers increased insertion and extraction forces, increased possibility of contact failure, and degraded operability and reliability attributable to the influence of dirt and dust. On this account, an alternative idea is to transfer data in a serial manner. When serial data is transferred in the block transmission mode, with the intention of efficient data transfer, the volume of transaction data in a block is constant, i.e., fixed-length block transmission, which compels the information processor to access to a certain amount of data regardless of the data volume in need. This is unfavorable for the information processor in expending idle time for making access to a piece of data (minimal unit data) in a specific address.
This impropriety may be avoided by transferring the address and data in pair in a serial manner, and data in a specific address can be accessed in a shorter time, but at the expense of increased time for transferring a large volume of data.